Smile has published a follow-up article with a statement that includes clarification on their support of TextExpander 5:

For those who prefer to stay with TextExpander 5 for now, we intend to support it on El Capitan and the next major upgrade of OS X […]
Beyond that, neither we nor anyone else know what to expect of Apple or OS X. We also hope to encourage you to join the new TextExpander at some point in the future.

I'm pleased to see that Smile were quick to respond to some of the concerns surrounding the release of TextExpander 6 and the move to a subscription model, and that they intend to support TextExpander 5 in the next version of OS X.

Give that OS X currently operates on an annual release schedule1, and usually arrives at the end of summer, TextExpander 5 has about 15-18 months left, at best. That's not the worst prognosis, though I am concerned about their "intent" of support. Intentions are not commitments, and while Smile may want to support TextExpander 5 in the next version of OS X, if an update like OS X 10.12.12 causes the app to stop working, it's not certain if Smile will actually fix it or just call it a day.

What I do find concerning is that the follow-up makes no mention of continued support of TextExpander touch 3 for iOS. The app has been removed from the App Store, so it seems they've completely dropped support for it. This worries me for two reasons:

I use iOS almost exclusively, as do many others, so if the next update to iOS somehow breaks the app or the keyboard, there won't be a fix.

It's not certain what will happen to apps that make use of TextExpander's SDK for snippet support, when the SDK is updated. Will snippets continue to work and sync from TextExpander touch 3, or will any updates to the SDK require the new, subscription-based app? If it's the latter, then every time I update my apps, it could be the last time my snippets will work.

I realize I sound overly negative about TextExpander's move to subscription pricing. Don't get me wrong, I actually think the subscription model, when done well, is a great idea. I subscribe to a number of services, as well as support indie writers and developers through subscriptions and patronage.

When it comes to TextExpander, however, the reason for a subscription isn't compelling, nor does it make sense for individuals. Even in the follow-up, Smile were awkwardly attempting to explain how their own syncing service could be of benefit to individuals:

Everyone can benefit from sharing. People who work alone have peers, or belong to civic, volunteer, hobbyist, or church groups. Before now, none of them could share snippets with each other. Now, they can. And we’re doing our best to ensure they will.

Either Smile are going for the hard sell or they don't know the majority of their individual users at all.

If the rumors about the rebranding of OS X to macOS are true, the annual release cycle may be abolished–in favor of more frequent, smaller updates. ↩